1. Field of the Invention
The present invention relates to a method for modifying a film-forming surface of a substrate (hereinafter referred to as a base), which is capable of improving a base surface dependency to a film formation on the base, prior to the formation of the film by a thermal CVD (Chemical Vapor Deposition) method using a reactant gas (hereinafter referred to as "O.sub.3 /TEOS reactant gas") containing an ozone-containing gas containing ozone (O.sub.3) in oxygen (O) and tetra-ethyl-ortho-silicate (TEOS), and a manufacturing method for a semiconductor device using the same.
Here, the base surface dependency means that when an insulating film is formed on the surface of the base particularly by use of O.sub.3 /TEOS reactant gas, film formation rates differ depending on a difference of substances constituting the surface of the base exposed or the shapes of an acute angle portion and obtuse angle portion in concave and convex portions, or the surface of the insulating film is not flat due to an occurrence of fine unevenness on the formed insulating film, as shown in FIG. 1.
2. Description of the Prior Art
With recent progress in very high integration and multi-layered wiring of semiconductor devices, a demand has been made for development of a technique for forming an insulating film, which is excellent in flatness, embedment of a concavity (hereinafter referred to as concavity embedment) and step coverage, and which controls penetration of moisture and impurities. As a technology for forming the insulating film that meets the above demand, a CVD method using an O.sub.3 /TEOS reactant gas has been attracting attention.
In the case where a film is formed by the CVD method using the O.sub.3 /TEOS reactant gas, as the concentration of O.sub.3 is increased, a film with a higher quality can be obtained.
On the other hand, the state of the film thus formed strongly depends on the state of the surface of the base. The effect of the base surface dependency on the state of the surface of the base is not observed under a film formation condition where the concentration of O.sub.3 is low, however, the effect thereof clearly appears under a film formation condition where the concentration of O.sub.3 is high.
It should be noted that the O.sub.3 /TEOS reactant gas with a high concentration of O.sub.3 and a silicon dioxide (SiO.sub.2) film formed by the CVD method using this reactant gas are hereinafter referred to as a High O.sub.3 /TEOS reactant gas and a High O.sub.3 /TEOS CVD SiO.sub.2 film, respectively. Furthermore, the O.sub.3 /TEOS reactant gas with a low concentration of O.sub.3 and the silicon dioxide film formed by the CVD method using this reactant gas are hereinafter referred to as a Low O.sub.3 /TEOS reactant gas and a Low O.sub.3 /TEOS CVD SiO.sub.2 film, respectively. Still furthermore, the silicon dioxide film formed by the CVD method using the O.sub.3 /TEOS reactant gas of any concentration of O.sub.3 is hereinafter simply referred to as an O.sub.3 /TEOS CVD SiO.sub.2 film.
FIG. 1 is a cross-sectional view showing abnormal growth of a film due to the effects of the base surface dependency.
As is shown in FIG. 1, a base surface dependency on the surface of the substrate 101 on which a film is to be formed (hereinafter referred to as a film-forming substrate) influences the surface of a High O.sub.3 /TEOS CVD SiO.sub.2 film 4, causing the surface of the film 4 to be uneven. At the same time, voids occur in the High O.sub.3 /TEOS CVD SiO.sub.2 film 4. It should be noted that the film-forming substrate 101 is composed of a semiconductor substrate 1, a base insulating film 2 formed thereon and wirings 3a and 3b formed on the base insulating film 2.
The methods shown in FIGS. 2A to 2D have heretofore been employed in order to remove the base surface dependency. The same elements as those shown in FIG. 1 are denoted by the same reference numerals.
The methods are:
(i) irradiating the film-forming surface of the substrate 101 with plasma (FIG. 2A); PA1 (ii) covering the film-forming surface of the substrate 101 with a plasma CVD SiO.sub.2 film 5 (FIG. 2B); PA1 (iii) forming a Low O.sub.3 /TEOS CVD SiO.sub.2 film 6 as the base before the High O.sub.3 /TEOS CVD SiO.sub.2 film (FIG. 2C); and PA1 (iv) forming the Low O.sub.3 /TEOS CVD SiO.sub.2 film 6 having thin thickness, irradiating the surface thereof with plasma, followed by forming the High O.sub.3 /TEOS CVD SiO.sub.2 film (FIG. 2D). It should be noted that the above methods (iii) and (iv) use a double-layer composed of the Low O.sub.3 /TEOS CVD SiO.sub.2 film 6 and the High O.sub.3 /TEOS CVD SiO.sub.2 film.
However, each of the conventional methods for modifying the film-forming surface of the substrate as given in above (i) to (iv) has the following problems, respectively.
(i) In the method using plasma irradiation, the conditions under which the effects of controlling the base surface dependency appears are not uniform. Accordingly, unification or standardization of the modification conditions by plasma irradiation cannot be achieved in all kinds of the film-forming surfaces of the substrates, but optimization is required as occasion demands. Furthermore, this method additionally requires a plasma enhances CVD apparatus for the plasma irradiation.
(ii) In the modifying method by covering the film-forming surface of the substrate with the plasma CVD SiO.sub.2 film 5, the plasma CVD SiO.sub.2 film 5 which is very compatible with the High O.sub.3 /TEOS CVD SiO.sub.2 film may be obtained depending on the conditions for film formation by the plasma enhanced CVD method. Accordingly, using the plasma CVD SiO.sub.2 film to cover the film-forming surface of the substrate, the High O.sub.3 /TEOS CVD SiO.sub.2 film of excellent quality can be obtained. However, the plasma CVD SiO.sub.2 film 5 is intrinsically poor in step coverage, and therefore the plasma CVD SiO.sub.2 film 5 is not suitable for a micronized pattern. Furthermore, the plasma enhanced CVD apparatus is additionally required for plasma irradiation.
(iii) In the method of covering the film-forming surface of the substrate with the Low O.sub.3 /TEOS CVD SiO.sub.2 film 6, the Low O.sub.3 /TEOS CVD SiO.sub.2 film 6 is very compatible with the High O.sub.3 /TEOS CVD SiO.sub.2 film, and the base surface dependency can be removed by covering the film-forming surface of the substrate with the Low O.sub.3 / TEOS CVD SiO.sub.2 film 6. However, the Low O.sub.3 TEOS CVD SiO.sub.2 film 6 has isotropic properties and a thickness of at least 100 nm is necessary as the base in this case. Therefore, the Low O.sub.3 /TEOS CVD SiO.sub.2 film 6 is not suitable for the micronized pattern.
On the other hand, another method for removing the dependency on the film-forming surface of the substrate has also been attempted. This method uses the O.sub.3 /TEOS CVD SiO2 film, instead of the Low O.sub.3 /TEOS CVD SiO.sub.2 film 6, as the base under low pressure. However, using the O.sub.3 /TEOS CVD SiO.sub.2 film under low pressure is substantially the same as using the Low O.sub.3 /TEOS CVD SiO.sub.2 film 6. Accordingly, using the O.sub.3 /TEOS CVD SiO.sub.2 film under low pressure is not suitable for the micronized pattern for the same reason that applies to the Low O.sub.3 /TEOS CVD SiO.sub.2 film 6.
Furthermore, the O.sub.3 /TEOS CVD SiO.sub.2 film under a Low O.sub.3 atmosphere and low pressure is inferior to the High O.sub.3 /TEOS CVD SiO.sub.2 film in quality.
(iv) The method of covering by the Low O.sub.3 /TEOS CVD SiO.sub.2 film 6 and irradiating the surface of the film with plasma is not suitable for the micronized pattern and makes manufacturing steps of the semiconductor device complicated.
Thus, all in all, the conventional methods for modifying a surface of a base are not so suitable for covering a narrow and deep concavity. Accordingly, the high integration of the semiconductor devices have been desired nowadays, and formations of an interlayer insulating film and a cover insulating film with a high quality by using a film forming method by the CVD method have been desired. In particular, covering the narrow and deep concavity has been desired.